PNITEB8ITY  OF   C  ALIFORM  I A   PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


Methods  of  Harvesting  and  Irrigation  in 
Relation  to  Moldy  Walnuts 


BY 
L.   D.  BATCHELOR 


BULLETIN  No.  367 

June,  1923 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY,  CALIFORNIA 

1923 


David  P.  Barrows,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS   OF   DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

Edward  J.  Wickson,  Horticulture  (Emeritus).  4 

,  Director  of  Resident  Instruction. 

C.  M.  Haring,  Veterinary  Science;  Director  of  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

C.  B.  Hutchison,  Plant  Breeding;  Director  of  the  Branch  of  the  College  of 

Agriculture,  Davis. 

H.  J.  Webber,  Sub-tropical  Horticulture;  Director  of  Citrus  Experiment  Station. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Ralph  E.  Smith,  Plant  Pathology. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
Walter  Mulford,  Forestry. 
James  T.  Barrett,  Plant  Pathology. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
W.  L.  Howard,  Pomology. 
*Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  R.  Hoagland,  Plant  Nutrition. 
G.  H.  Hart,  Veterinary  Science. 

L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

CITRUS  EXPERIMENT  STATION 

division  of  orchard  management 

L.  D.  Batchelor  Ralph  G.  LaRue 

J.  G.  Surr  E.  R.  Parker 


*  In  cooperation  with  Division  of  Agricultural  Engineering,  Bureau  of  Public  Roads,  U.  S. 
Department  of  Agriculture. 


METHODS  OF  HARVESTING  AND  IRRIGATION 
IN  RELATION  TO  MOLDY  WALNUTS* 


By  L.  D.  BATCHELORt 


CONTENTS  page 

Introduction 677 

Seriousness  and  Distribution  of  the  Mold 677 

Specific  Fungi  Causing  Moldy  Nuts 679 

Appearance  of  Mold  on  Walnut  Kernels 680 

Entrance  of  Mold  into  Nuts 680 

Occurrence  of  Mold  in  Seedling  and  Budded  Nuts 681 

Variation  Among  Seedling  Trees 682 

Extent  of  Variation 682 

Likelihood  of  Individual  Trees  Producing  Moldy  Nuts  Year  after  Year 683 

Relation  of  Mold  to  Side-Blighted  Nuts 683 

Relation  of  Condition  of  Nuts  at  Harvest  to  Presence  of  Mold 684 

Maturity  of  Nuts 684 

Mold  Increase  as  Harvest  Advances 685 

More  Mold  Among  Stick-Tights  than  Clean  Nuts 686 

Relation  of  Delay  in  Harvesting  to  Percentage  of  Moldy  Nuts 687 

Relation  of  Sunburned  Nuts  to  Prevalence  of  Mold 690 

Relation  of  Curing  to  Percentage  of  Moldy  Nuts 692 

Relation  of  Irrigation  to  Percentage  of  Moldy  Nuts 692 

Summary .' 695 

Practical  Recommendations 695 


INTRODUCTION 

SERIOUSNESS  AND  DISTRIBUTION  OF  THE  MOLD 

For  many  years  the  prevalence  of  mold  on  walnut  kernels  has 
been  one  of  the  important  causes  of  reduction  in  grade  of  nuts  and 
therefore  of  loss  of  money  to  the  walnut  growers.  A  dark  discolora- 
tion of  the  kernels  is  frequently,  but  not  invariably,  associated  with 
the  mold.  In  certain  sections  this  trouble  has  been  very  bad  the 
past  three  or  four  years. 


*  Paper  No.  109,  University  of  California,  Graduate  School  of  Tropical  Agri- 
culture and  Citrus  Experiment  Station,  Riverside,  California. 

t  The  author  wishes  to  express  his  sincere  appreciation  for  the  many  helpful 
suggestions  in  regard  to  this  investigation,  made  by  Dr.  J.  T.  Barrett,  Professor 
R.  S.  Vaile  and  Mr.  Carlyle  Thorpe.  The  arduous  task  of  cracking  thousands 
of  nuts  to  obtain  data  was  accomplished  by  the  cooperation  of  Mr.  D.  C.  Wylie 
of  the  Field  Department  of  the  California  Walnut  Growers'  Association. 


678  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  extreme  coastal  districts  and  the  hot  inland  regions  have 
not  been  seriously  troubled  with  mold.  In  the  intermediate  sections 
both  the  mold  and  the  black  kernels  have  frequently  given  a  great 
deal  of  trouble.  The  hot  inland  valley  sections  may  be  troubled 
with  a  high  per  cent  of  black  kernels  even  in  the  absence  of  mold. 
The  most  serious  trouble  with  moldy  nuts  is  usually  found  on  sandy 
soils. 

The  economic  loss  to  the  walnut  grower  can  be  realized  by  calling 
to  mind  the  fact  that  a  percentage  of  over  10  per  cent  of  poor  nuts 
in  any  lot  will  necessitate  the  sale  of  the  whole  lot  as  near-grades,1 
at  a  probable  reduction  of  30  to  35  per  cent  of  the  value  of  first- 
class  nuts,  the  exact  value  depending  upon  the  actual  percentage 
of  poor  nuts. 

A  further  reduction  in  the  percentage  of  good  nuts  to  less  than 
75  per  cent  good,  will  necessitate  the  whole  lot  being  sold  as  culls 
at  a  loss  of  another  30  per  cent  or  more  of  the  value  of  good  nuts. 
The  three  grades  of  Santa  Barbara  soft-shell  seedlings,  sold  by  the 
California  Walnut  Growers'  Association  during  the  season  of  1921- 
1922,  returned  the  following  prices  to  the  growers:  The  first  grade 
('Diamond  Brand')2  $24.50  per  hundred  pounds;  the  near-grades 
averaged  close  to  $15.00  per  hundred  pounds,  and  the  culls  $7.00 
per  hundred  pounds. 

It  should  not  be  inferred  that  all  the  nuts  in  the  inferior  classes 
are  poor  quality  nuts,  but  rather  that  the  percentage  of  poor  nuts 
in  the  near-grades  and  culls  is  too  large  compared  with  the  good 
nuts  to  justify  their  being  sold  as  a  first-class  product.  It  should 
be  clear  from  this  discussion  that  it  takes  only  a  relatively  small 
percentage  of  inferior  nuts  to  lower  the  grade  and  the  value  of  a 
lot  of  nuts,  the  majority  of  which  are  of  a  good  quality.  If  a  given 
lot  of  nuts  is  near  the  border  line  between  the  above  grades,  only 
one  or  two  pounds  of  moldy  nuts  per  hundred,  may  change  the  com- 
mercial value  of  the  whole  lot  $7.00  to  $8.00  per  hundred  pounds. 
Most  of  the  moldy  nuts  cannot  be  sorted  out  in  the  packing  house; 
thus  great  losses  have  been  experienced  in  the  past  which  were 
unavoidable  by  any  means  of  grading  or  sorting  practiced  up  to  the 
present  time. 


I'Near  Grades'  are  an  inferior  commercial  grade  in  which  the  good  nuts 
comprise  only  75  per  cent  to  89  per  cent  of  the  total.  The  rest  are  moldy, 
shriveled,   sun-burned,    and    generally   inedible. 

2 'Diamond  Brand.'  is  the  trade  name  for  the  best  grade  of  nuts  shipped 
by  The  California  Walnut  Growers'  Association  and  is  guaranteed  to  contain 
at  least  90  per  cent  perfect  nuts. 


Bulletin  367]     harvesting  and  irrigation  of  moldy  walnuts         670 

The  efforts  of  the  walnut  growers  during  a  period  of  practically 
a  year  are  expended  on  producing  high-grade  nuts.  Good  nuts  can 
be  changed  like  magic  into  the  cull  class  in  a  week  or  ten  days  of 
improper  handling.  The  work  herein  reported  has  shown  that  the 
nuts  which  are  finally  graded  as  culls  because  of  mold  or  dark  kernels, 
were  without  question  first-class  nuts  at  their  maturity,  a  period 
which  should  coincide  with  the  beginning  of  the  normal  harvest  season. 


SPECIFIC  FUNGI  CAUSING  MOLDY  NUTS 

The  particular  fungi  which  cause  the  mold  in  walnuts  have  been 
studied  during  the  past  three  years  by  Dr.  J.  T.  Barrett  of  Citrus 
Experiment  Station,  Riverside,  to  whom  the  writer  is  indebted  for  the 
following  statements: 

"Mold  in  walnuts  is  not,  strictly  speaking,  a  specific  disease, 
therefore,  not  necessarily  confined  to  the  action  of  a  single  specific 
organism.  Many  fungi  and  bacteria  may  grow  for  a  time,  upon 
matured  parts  of  plants  which  offer  suitable  conditions  of  moisture 
and  nutrient  material,  without  actually  destroying  much  of  the  tissue. 
The  checking  of  the  favorable  conditions  checks  the  growth  of  the 
organism.  Therefore,  it  was  no  surprise  to  find  that  several  fungi 
could  cause  moldy  walnuts.  No  doubt  many  others  would  produce  a 
similar  effect  were  they  present  in  the  groves  in  sufficient  quantity, 
and  at  a  time  when  the  nuts  were  in  the  proper  stage  for  infection. 

"Determination  of  the  fungi  most  commonly  associated  with 
the  moldy  nuts  was  by  means  of  cultures  made  by  transferring 
pieces  of  the  mold  or  mold-bearing  tissue  of  the  kernel  to  a  suitable 
nutrient  medium,  usually  glucose  potato-extract  agar.  Usually  within 
a  week  to  ten  days  sufficient  growth  had  taken  place  to  make  the 
determination  possible.  The  many  cultures  made  represented  sample 
collections  of  nuts  from  more  than  twenty-five  groves  distributed 
in  twelve  of  the  main  walnut-growing  sections. 

"The  result  of  these  studies  revealed  that  by  far  the  most  preva- 
lent fungus  in  moldy  nuts  is  Alternaria,  a  genus  containing  many 
species,  some  of  which  cause  very  serious  diseases  of  plants,  many 
others  occurring  as  saprophytes  only.  A  little  more  than  seventy- 
six  per  cent  of  the  total  number  of  nuts  cultured  were  infected  with 
Alternaria.  Less  than  one  per  cent  showed  some  other  fungus  asso- 
ciated with  the  Alternaria.  While  no  attempt  has  yet  been  made  to 
determine  the  species,  the  character  of  growth  and  spores  in  the 
majority  of  the  cultures  examined  indicates  that  one  species  princi- 
pally occurs. 


080  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

"The  largest  number  of  cultures  were  made  from  nuts  collected 
from  the  six  districts  most  seriously  troubled  with  moldy  nuts.  It 
is  interesting  to  note  that  eighty-five  per  cent  of  these  cultures 
developed  Alternaria. 

"Several  other  fungi  were  found  in  moldy  nuts,  but  not  at  all 
consistently,  and  in  a  number  of  cases  ranging  from  one-half  to 
five  per  cent  of  the  total  number  of  cultures. 

"The  genera  represented  are  Penicillium  (blue  and  green  mold), 
Cladosporium,  Fusarium,  Macrosporium  (very  similar  to  Alternaria), 
Mucor,  and  Sclerotinia  (form  with  small  sclerotia).  About  five 
per  cent  of  the  cultures  were  negative,  and  two  per  cent  developed 
fungi  that  were  sterile  and  not  determined. 

"While  these  studies  to  date  are  of  a  rather  preliminary  character, 
the  evidence  is  sufficient  to  indicate  very  strongly  that  the  fungus 
genus  most  responsible  for  the  moldy  nuts,  during  the  past  three 
years  is  Alternaria.  How  many  species  are  concerned  has  not  been 
determined.  This  with  a  number  of  other  phases  of  the  problem 
is  to  be  further  studied." 

APPEARANCE    OF    MOLD    ON    WALNUT    KERNELS 

In  the  worst  cases  of  mold  the  abundance  of  fungous  growth, 
known  as  mycelium,  is  seen  as  a  light  to  grayish-colored  cottony 
growth  on  the  kernels  and  inner  walls  of  the  shell.  If  the  growth 
is  only  slight  and  largely  confined  to  the  diaphragm  of  the  shell, 
it  may  not  be  detected.  On  the  other  hand,  by  the  aid  of  a  magni- 
fying glass,  strands  of  fungous  mycelium  may  be  detected  on  the 
kernel  of  many  first-grade  nuts,  indicating  that  under  suitable  condi- 
tion most  nuts  would  probably  be  subject  to  infection. 

On  the  drying  of  the  nuts  the  mold  dries  also,  but  does  not  by 
any  means  disappear.  It  retains  its  fluffy  appearance  but  may 
collapse  somewhat  on  removal  of  the  shell.  There  is  not  a  marked 
difference  in  appearance  of  most  of  the  various  mold  fungi  as  seen 
on  the  kernel.  Sclerotinia  and  Fusarium  are  usually  distinguishable 
from  Alternaria,  Macrosporium,  and  Cladosporium,  although  one 
may  be  frequently  mistaken. 

ENTRANCE   OF   MOLD   INTO  NUTS 

Among  the  many  thousand  nuts  which  have  been  cracked  and 
examined  in  connection  with  these  studies,  no  mold  has  been  found 
in  a  nut  which  at  the  time  of  examination  was  incased  in  a  sound 
husk   free   from   visible    cracks   and   in    crisp    condition    free   from 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS  681 

decay.  The  mold  commonly  starts  to  grow  in  the  cracks  of  the 
husk  which  accompany  maturity,  and  spreads  thence  to  the  lining 
of  the  husk;  it  quickly  spreads  through  the  base  and  suture  of  the 
nut  and  thence  to  the  diaphragm,  and  the  pellicle  of  the  kernel. 

Nuts  frequently  drop  to  the  ground  with  the  green  husk  intact. 
If  such  nuts  lie  on  the  ground  a  few  days  the  husks  begin  to  decay. 
Alternaria  is  the  most  common  cause  of  this  decay.  A  soft  and 
decayed  spot  usually  first  appears  on  the  apex  of  the  shuck.  In 
such  cases  the  mold  spreads  to  the  kernel  by  passing  through  the 
suture  at  apex  of  the  nut. 

Even  in  the  worst  cases  of  mold  the  fungus  is  superficial  on  the 
pellicle  and  does  not  actually  affect  the  eating  qualities  of  the  kernel 
except  as  it  presents  an  inedible  appearance. 


OCCUEEENCE  OF  MOLD  IN  SEEDLING  AND  BUDDED  NUTS 

The  trouble  with  mold  has  been  much  worse  among  the  seedling 
groves  than  in  the  'budded'3  ones.  This  difference  is  mainly  due 
to  the  fact  that  the  budded  varieties  are  more  apt  to  drop  the  nuts 
from  the  tree  free  from  the  husk. 

Many  of  the  old  seedling  trees  are  characterized  by  a  high  per- 
centage of  the  nuts  dropping  as  green  'stick-tights.'4 

The  seedlings  which  more  nearly  approach  the  paper-shell  type 
are  more  likely  to  shed  the  nuts  as  green  stickers  than  the  typical 
Santa  Barbara  soft-shell  type. 

The  budded  varieties,  especially  of  the  Santa  Barbara  soft-shell 
type  such  as  Placentia  and  Chase,  are,  however,  not  entirely  free 
from  this  trouble.  Moldy  nuts  have  occurred  among  both  of  these 
varieties  to  a  serious  degree,  when  for  one  reason  or  another  the 
conditions  have  been  favorable  to  mold  development.  The  fact  that 
the  nuts  of  budded  varieties  usually  drop  free  from  the  shucks  is 
not  the  only  factor  which  lessens  the  likelihood  of  mold  among  this 
class  of  nuts.  Another  reason  is  the  fact  that  the  majority  of  the 
budded  groves  are  younger  than  the  seedling  groves,  and  for  that 
reason  are  not  as  apt  to  become  drought-stricken  during  the  growing 
season  as  the  older  trees.  As  will  be  shown  later,  there  is  a 
correlation  between  drought  and  mold. 


s  The  term  'budded'  walnut  tree  is  a  trade  name  to  designate  the  most 
desirable  commercial  varieties  of  nuts  which  may  be  propagated  by  budding 
or  grafting  them  on  black  walnut  roots. 

4  The  term  ' stick-tight'  has  become  universally  used  by  walnut  growers 
to  designate  the  nuts  which  drop  to  the  ground  with  the  husks  sticking  to 
them. 


682 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


VARIATION  AMONG  SEEDLING  TREES 

EXTENT  OF  VARIATION 
A  group  of  eighty  seedling  trees  have  been  under  observation 
for  the  past  three  years.  The  prevalence  of  moldy  nuts  produced 
by  the  respective  trees  has  varied  greatly  each  year.  The  range 
and  mean  per  cent  of  moldy  nuts  per  tree  are  shown  in  table  1.  At 
least  fifty5  nuts  per  tree  were  examined  in  each  sample. 


TABLE  1 
Range  of  Variation  and  Mean  Per  Cent  of  Mold  Found  in  Nuts  from  a  Group 

of  Seedling  Trees 


Total  per  cent  of  mold  in  clean  nuts 

Year 

Range  among  individual 
trees 

Mean  of  all 
trees 

1920 

0—56 
0—24 
0—48 

16 

1921 

7 

1922 

11 

It  is  very  apparent  from  table  1  that  a  group  of  seedling  trees 
is  an  extremely  variable  population  as  regards  this  character  of 
susceptibility  of  the  nuts  to  mold.  One  tree  may  produce  nuts 
which  are  free  from  mold,  while  possibly  the  adjacent  tree  produces 
20  to  50  per  cent  moldy.  Some  of  the  wide  variation  is  probably 
due  to  the  inherent  tendency  of  certain  trees  to  produce  stick-tight 
nuts,  which  are  more  apt  to  mold  than  clean  nuts. 

Some  of  the  apparent  variation  in  the  percentage  of  moldy  nuts 
from  different  trees  may  be  due  to  the  impracticability  of  harvest- 
ing the  crop  from  each  seedling  tree  when  the  nuts  are  in  exactly 
the  same  state  of  maturity.  Again  the  variation  in  the  soil  and 
subsoil  makes  it  impossible  to  have  the  available  moisture  in  the 
root  zone  of  each  individual  tree  alike.  Such  a  variation  in  moisture 
is  bound  to  be  reflected  in  maturity  of  the  crop,  especially  in  the 
ease  with  which  the  nuts  are  husked,  with  a  consequent  prevalence 
of  mo1  (I.  From  a  practical  point  of  view,  it  is  important  to  know 
that  some  particular  trees  are  much  more  likely  to  produce  moldj* 
nuts  than  others,  as  it  may  become  advisable  to  segregate  the  moldy 
nuts  in  the  orchard. 

5  It  was  found  by  experience  that  a  sample  of  fifty  nuts  gave  practically 
as  accurate  results  as  one  hundred  or  more,  provided  the  respective  lot  from 
which  the  sample  was  drawn  was  properly  mixed,  so  the  laws  of  chance 
came  into  fair  play. 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS  683 


LIKELIHOOD  OF  INDIVIDUAL  TREES  PEODUCING 
MOLDY  NUTS  YEAE  AFTEE  YEAE 

The  probability  that  certain  trees  may  produce  a  large  per  cent 
of  moldy  nuts  year  after  year  has  been  shown  to  only  a  small  degree 
by  the  studies  of  the  past  three  years.  Even  though  there  is  a  small 
correlation  between  the  percentage  of  moldy  nuts  from  individual 
trees,  comparing  one  year  with  another,  there  are  many  exceptions 
to  this  general  rule.  A  strict  interpretation  of  the  statistical  data6 
at  hand  not  only  shows  the  uncertainty  of  foretelling  the  relative 
amount  of  mold  from  individual  trees  in  the  future  from  records 
of  the  past;  but  the  harvesting  and  curing  experiments  herein  set 
forth  show  that  these  last  mentioned  factors  are  largely  responsible 
for  the  prevalence  of  favorable  mold-producing  conditions. 


RELATION  TO  SIDE-BLIGHTED  NUTS 

Inasmuch  as  the  mold  organism  usually  enters  the  husk  after 
it  starts  to  crack,  it  was  thought  that  the  mold  might  enter  the  small 
fissures  in  the  husk  caused  by  the  form  of  walnut  blight  commonly 
known  as  side-blight.  Many  nuts  which  are  side-blighted  to  a  slight 
extent  mature  as  good  nuts,  even  though  the  husk  may  be  affected 
with  blight.  Such  blight  cankers  may  not  fully  penetrate  the  husk 
sufficiently  to  stain  the  shell  of  the  nut,  even  though  the  husk  is 
clearly  ruptured  by  the  blight. 

During  the  middle  of  the  1922  growing  season,  a  large  number  of 
side-blighted  nuts  were  covered  with  gauze  bags  so  the  nuts  could 
be  identified  at  harvest  time.  Likewise  an  equal  number  of  healthy 
nuts  were  covered.  Upon  examination  at  harvest  time  the  blighted 
nuts  showed  a  slightly  higher  per  cent  of  moldy  nuts  than  the 
healthy  nuts.  The  difference  was  more  marked  among  stick-tight 
nuts  than  those  which  dropped  free  from  the  husks.  A  larger  per  cent 
of  the  side-blighted  nuts  were  finally  stick-tights  than  in  the  case  of 
the  healthy  nuts. 


6  A  detailed  presentation  of  the  statistical  data  is  not  called  for  at  this  ttme. 
It  is  sufficient  to  state  here  the  correlation  coefficients  for  the  per  cent  of 
moldy  nuts  per  individual  tree  in  both  clean-nut  and  stick-tight  classes  were 
calculated,  comparing  the  following  harvest  seasons:  1920  with  1921;  1920 
with  1922;  1921  with  1922.  Although  all  six  coefficients  were  positive,  the 
low  average  of  only  .33  with  a  probable  error  of  .07  shows  only  a  low  degree 
of  probability  that  a  tree  will  produce  markedly  moldy  nuts  year  after  year, 
other  factors  being  equal. 


684 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Although,  there  is  a  positive  association  of  side-blight  and  mold, 
it  is  doubtful  if  this  is  a  very  important  factor.  Where  there  is 
a  large  enough  percentage  of  mold  to  be  a  serious  commercial  con- 
sideration, the  majority  of  cases  become  infected  by  other  means 
than  through  blight  cankers  in  the  husks. 


RELATION  OF  CONDITION  OF  NUTS  AT  HARVEST 

TO  PRESENCE  OF  MOLD 

MATUEITY  OF  NUTS 

The  relation  of  the  mold  to  the  progress  of  the  ripening  of  the 
nuts  was  suggested  from  the  records  of  1920.  This  investigation 
also  showed  a  possible  relation  of  harvesting  methods  to  moldy  nuts. 
Twelve  thousand  nuts  were  cracked  to  obtain  this  test,  relative  to 
the  relation  of  harvest  methods  to  moldy  nuts.  The  nuts  were 
equally  divided  into  three  lots:  First,  nuts  which  were  picked  from 
the  trees  when  matured  so  the  husks  were  starting  to  crack;  second, 
clean  nuts  from  ground;  and  third,  stick-tights,  the  husks  of  some 
of  which  were  black  and  dry  when  they  fell,  while  others  were 
originally  mushy  but  had  lain  around  until  the  husks  were  dried 
up.  The  percentage  of  mold  in  these  three  classes  is  shown  in 
table  2. 

TABLE  2 

Progress  of  Mold  Development  in  Nuts  at  Different  Stages  of  Maturing, 

and  Conditions  at  the  Same  Date  of  Harvest  (1920  Crop) 


Classification 

Moldy 
culls 

Moldy  but 
passable 

Total 
mold 

Nuts   picked   from   trees   when   husks 
started  to  crack 

6% 

4% 

10% 

Clean  nuts  from  the  ground 

7%' 

8% 

15% 

Black  stick-tight  nuts  from  ground 

13% 

14% 

■  27%.   •  :. 

The  moldy  nuts  were  divided  into  two  classes  according  to  the 
amount  of  mold  present:  (a)  moldy  culls;  (b)  moldy  but  passable. 
Tn  the  latter  class  the  mold  was  clearly  visible  on  the  kernels,  but 
not  bad  enough  to  condemn  them  as  culls.  At  the  same  time  there 
was  a  certain  additional  percentage  of  nuts  which  showed  only  such 
small  traces  of  mold  that  they  were  classed  as  first-class  nuts. 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS 


685 


It  is  clear  from  a  study  of  the  summary  that  a  delay  in  harvest- 
ing is  bound  to  permit  the  mold  to  increase.  Even  the  nuts  picked 
from  the  trees  were  10  per  cent  moldy.  As  some  of  this  mold  was 
passable,  however,  it  would  not  have  barred  them  from  the  best 
grade  if  they  had  all  been  periodically  harvested  as  soon  as  the  husks 
cracked.  Many  of  the  nuts  in  the  lots  picked  off  the  trees  had  been 
held  in  the  clasp  of  the  partly  opened  husks  for  several  days.  The 
prompt  harvesting  of  the  nuts  would  have  prevented  the  develop- 
ment of  the  mold,  and  have  made  the  whole  crop  grade  as  Diamond 
Brand.  A  delay  of  several  weeks  would  have  allowed  the  whole 
crop  to  become  so  moldy  that  it  would  have  graded  as  near-grades 
or  culls.  This  point  is  brought  in  again  in  several  of  the  following 
summaries : 

MOLD  INCREASE  AS  HARVEST  SEASON  ADVANCES 
(Harvested  according  to  ordinary  methods) 

Harvest  and  cracking  records  were  kept  from  a  group  of  trees 
near  Anaheim  during  1922.  The  nuts  were  picked  up  three  or 
four  times  between  September  28  and  November  1.  The  trees  were 
shaken  each  time,  except  at  the  first  picking.  One  hundred  nuts 
per  tree  were  cracked  at  each  picking  to  determine  the  amount  of 
mold  in  the  clean  and  stick-tight  nuts.  Table  3  shows  the  increase 
in  the  percentage  of  mold  as  the  harvest  season  advanced. 

TABLE  3 

Increase  in  Percentage  of  Moldy  Nuts  as  the  Harvest  Season  Advanced 


,               1st  pick 

(Sept.  23-28) 

2d  pick 
(Oct.  10-14) 

3d  pick 
(Oct.  25-Nov.  1) 

Moldy 
culls 

Moldy 

but 
passable 

Moldy 
culls 

Moldy 

but 
passable 

Moldy 
culls 

Moldy 

but 

passable 

Clean  nuts 

3% 
9% 

6% 
16% 

5% 

4% 
12% 
23% 

9% 

18% 
27% 

4% 
15% 

10% 

Dry  stick-tights 

28  % 

Green  stick-tights 

,     Table  3 .  as  well  as  table  2  shows  that  the  dry  stick-tight  nuts 
are  much  more  likely  to  be  moldy  than  clean  nuts. 

This  is  again  brought  out  in  table  4  which  shows  a  summary  of 
the  records  of  all  three  years.  The  main  purpose  of  table  3,  how- 
ever, is  to  show  the  increase  in  percentage  of  moldy  nuts  as  the 
season  advances. 


686  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

With  the  clean  nuts  and  the  black,  dry  stick-tights  there  was 
an  increase  in  moldy  nuts,  comparing  the  first  pick  with  the  second 
one.  Still  further  increase  of  mold  was  noted  in  the  black  stick- 
tights  between  the  second  and  third  picks. 

This  big  increase  in  mold  is  bad  enough  in  the  clean  nuts  and 
black  stick-tights,  but  an  even  greater  increase  is  shown  by  the 
green  stick-tights. 

This  last  mentioned  class  of  nuts  was  practically  free  from  moldy 
culls  at  the  first  picking.  Twelve  to  fourteen  days  later,  when  the 
trees  were  shaken  for  the  first  time,  the  green  stick-tights  were  50 
per  cent  moldy  with  23  out  of  every  100  nuts  reduced  to  moldy 
culls.  Some  of  the  green  stick-tights  of  this  second  pick  were  already 
on  the  ground  before  the  trees  were  shaken.  Possibly  50  per  cent 
of  them  were  shaken  off. 

It  is  interesting  to  note  what  100  pounds  of  the  green  stick-tights 
were  worth  at  the  first  pick  compared  with  the  second  one. 

With  such  nuts  originally  grading  as  Diamond  Brand  when 
properly  harvested,  they  were  worth  $22.50  per  100  pounds.  Although 
there  were  50  pounds  of  good  nuts  in  every  100  pounds  of  the  second 
pick,  they  could  not  be  sorted  out  of  the  near-grades  and  culls.  At 
the  very  best  the  whole  lot  could  scarcely  be  counted  on  to  grade 
as  near-grades,  valued  at  $15.00  or  less  per  100  pounds.  A  few 
more  days  delay  in  harvesting  would,  no  doubt,  have  made  culls 
of  them,  worth  possibly  $7.50.  It  is  only  a  matter  of  combining 
plain  arithmetic  and  good  judgment  to  see  that  it  would  pay  big 
dividends  to  speed  up  the  harvest  of  green  stick-tights,  even  to  the 
extent  of  spending  fifty  cents  per  100  pounds  or  more  as  an  extra 
bonus  for  harvesting  and  shucking  this  type  of  nuts.  It  would 
also  require,  no  doubt,  more  personal  supervision  of  the  laborers 
by  the  grove  owner,  which  is  a  good  thing  on  general  principles, 
and  would  be  well  paid  for  in  such  a  case  as  above  illustrated. 

MORE  MOLD  AMONG  STICK-TIGHTS  THAN  CLEAN  NUTS 

In  tables  2  and  3  it  has  already  been  shown  that  stick-tights 
are  more  apt  to  be  moldy  than  are  clean  nuts.  The  following  table 
summarizes  the  observations  for  all  three  years.  With  the  large 
number  of  nuts  observed  (28,451)  to  make  this  comparison,  the 
small  errors  of  sampling,  and  the  personal  errors  of  judgment  have 
been  leveled  by  the  laws  of  chance.  It  becomes  a  practical  certainty 
that  stick-tight  nuts  at  harvest  are  likely  to  include  somewhat  more 
than  twice  as  many  moldy  nuts  than  are  the  clean-shelled  nuts. 


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BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS 


687 


TABLE  4 

Percentage  of  Moldy  Nuts  in  Clean  and  Stick-Tight  Nuts 
(Result  of  28,451  counts) 


Class 

Moldy 
culls 

Moldy  but 
passable 

Total 
moldy  nuts 

Clean  nuts 

4% 

11% 

7% 
17% 

11% 

Stick-tights 

28% 

The  summary  in  table  4  includes  four  different  crops  from  two 
groves.  Nuts  from  120  trees  are  about  equally  represented  in  this 
summary.  In  all  cases  when  any  considerable  number  of  trees, 
say  from  8  to  20,  were  grouped  together,  the  trend  of  the  results, 
without  any  exception,  was  the  same  as  the  above.  Although  it  was 
clear  at  the  end  of  the  1921  season  that  most  of  the  moldy  culls 
traced  back  to  the  stick-tight  nuts,  it  was  equally  clear  that  a  certain 
amount  of  mold  occurred  in  the  ordinary  harvest  of  typical  clean- 
shucked  nuts. 

The  separation  of  these  two  classes  of  nuts  in  the  orchards  would 
no  doubt  lessen  the  trouble  in  grading  the  crop.  It  is  stopping 
short  of  the  real  issue,  however,  to  leave  the  question  here  without 
finding  out  more  about  the  cause  of  even  the  small  amount  of  mold 
in  the  clean  nuts.  The  work  was,  therefore,  enlarged  in  1922  to 
include  observations  on  the  relation  of  the  mold  to  harvesting  methods 
as  well  as  an  attempt  to  reduce  the  number  of  stick-tights,  and 
thus  the  large  amount  of  mold. 


RELATION  OF  DELAY  IN  HARVESTING  TO  PERCENTAGE 

OF  MOLDY  NUTS 

The  increase  in  per  cent  of  moldy  nuts,  heretofore  discussed  in 
table  3,  took  place  under  ordinary  harvesting  conditions.7  The  trees 
were  shaken  at  each  picking,  except  the  first  one,  and  all  the  nuts 
picked  up.  Most  of  this  increase  in  mold  took  place  while  the  nuts 
were  still  on  the  trees,  held  within  the  clasp  of  the  partly  opened 
husks. 

With  this  increase  in  mold  under  normal  conditions  of  harvest- 
ing, it  is  now  of  interest  to  see  what  takes  place  when  the  nuts  are 


7  The  nuts  are  gathered  two  or  three  times  by  the  ordinary  harvesting 
methods.  Frequently  the  nuts  are  allowed  to  lie  on  the  ground  in  the  grove 
from  a  week  to  ten  days  between  pickings. 


G88 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 


allowed  to  lie  on  the  ground  for  several  weeks,  as  they  often  do, 
under  slack  harvesting"  methods.  Several  trials  were  made  at  the 
beginning  of  the  1922  season.  Nuts  from  the  first  picking,  both 
clean  and  stick-tights,  were  left  on  the  ground  in  the  groves  to 
determine  the  effect  of  this  delay  of  harvesting  on  the  mold.  The 
first  counts  of  the  mold  were  made  when  the  nuts  would  ordinarily 
be  picked  up  (September  20  to  29).  The  second  count  from  the 
respective  groups  was  made  a  week  or  ten  days  afterward,  and  the 
third  count  (November  1),  at  the  end  of  the  harvest  period. 

The  rapid  increase  in  mold  is  shown  by  table   5,   which  sum- 
marizes the  results  of  two  tests. 


TABLE  5 

Eapid  Increase  in  Percentage  of  Moldy  Nuts  by  Delay  in  Harvesting  Nuts 

which  Fell  at  Beginning  of  Season  (Nuts  feom  First  Pick 

Left  on  Ground  in  Orchard) 


1st  crack 
(Sept.  28) 

2d  crack 
(Oct.  12) 

3d  crack 
(Oct.  21) 

Moldy 
culls 

Moldy  but 
passable 

Moldy 
culls 

Moldy  but 
passable 

Moldy 
culls 

Moldy  but 
passable 

Clean  nuts 

6% 

12% 

16% 

10% 

15% 

11% 

Black  stick-tights 

10% 

17% 

20% 

18% 

19% 

18% 

The  rapid  increase  in  the  mold  on  these  early  ripening  nuts 
occurred  during  the  first  week  or  ten  days  of  harvest.  After  this 
time  the  nuts  were  largely  cured  on  the  ground,  and  there  was  no 
increase  of  mold  from  then  until  the  end  of  the  season.  In  fact 
these  early  nuts  from  the  first  pick  were  changed  from  Diamond 
Brand  to  near-grades  by  a  delay  of  eight  to  ten  days  in  picking 
them  up.  On  the  other  hand,  the  third  picking  of  stick-tights  sum- 
marized in  table  3  shows  even  more  mold  than  the  stick -tights  just 
mentioned  which  laid  on  the  ground  for  nearly  forty  days.  This 
is  due  to  the  fact  that  most  of  this  last  class  tabulated  in  table  5 
were  dry  and  crisp '"  when  they  fell,  while  the  third  regular  pick 
included  many  mushy  stickers. 

This  brings  us  to  the  necessity  of  a  somewhat  clearer  under- 
standing of  stick-tights.  There  are  two  or  three  distinct  classes 
produced  by  as  many  distinct  causes  and  with  radically  different 
kinds  of  kernels  in  them. 


BULLETIN  3G7]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS 


680 


First,  there  are  the  dried-up  black-husked  stick-tights,  the  husk 
of  which  usually  turns  completely  black  while  hanging  on  the  tree. 
Such  stick-tights  are  caused  by  a  stem  rot  which  may  be  in  evidence 
as  early  as  the  middle  of  August.  Many  of  the  nuts  in  this  class 
are  borne  in  the  centers  of  the  trees,  a  fact  which  shows  that  their 
condition  has  no  relation  to  heat  or  sunburn.  Such  nuts  when  picked 
off  the  trees  usually  show  about  10  per  cent  moldy  culls,  and  from 
20  per  cent  to  40  per  cent  moldy  but  passable  kernels.  About  50 
per  cent  usually  show  good,  sound,  white  kernels.  The  kernels  in 
this  class,  as  a  whole,  are  not  quite  up  to  normal  plumpness.  No 
doubt  the  premature  stopping  of  the  growth  of  the  nut  by  the  rot 
of  the  stem  is  responsible  for  the  lack  of  plumpness. 

The  black,  dry  stick-tights  discussed  above,  however,  usually 
fail  to  account  for  many  of  the  dark-meated  culls,  and  the  high 
percentage  of  mold  that  may  be  found  under  certain  trees,  or  in 
certain  loads  of  near-grades  which  reach  the  packing-house.  With 
this  fact  in  mind,  a  close  account  was  kept  of  the  second  type,  the 
green  stick-tights,  during  the  1922  season.  The  green  stick-tights 
are  usually  associated  with  lack  of  late  summer  irrigation.  Many 
counts  of  the  mold  were  made  of  samples  of  these  green  stick-tights 
which  were  allowed  to  lie  on  the  ground  in  the  grove  until  they  became 
mushy.  This  mushy  condition  of  the  stick-tights  exists  all  too  often 
in  many  commercial  groves.  A  large  lot  of  green  stick-tights  were 
gathered  on  September  20,  and  will  serve  as  an  example  of  other 
similar  experiments.  A  sample  of  100  nuts  was  cracked  on  this 
date.  The  remainder  of  the  lot  were  left  in  the  grove  with  the 
husks  on  them  and  cracked  as  noted  in  table  6.  A  rapid  increase 
in  the  percentage  of  mold  followed  as  the  husks  became  mushy. 
Finally,  some  time  before  the  end  of  the  season,  the  husks  were 
completely  dried  up,  and  the  nuts  thus  resembled  the  black  stick- 
tights. 

TABLE  6 

Showing  Increase  in  Percentage  of  Moldy  Nuts  in  Green  Stick-Tights  Left 
in.  the  Grove  Through. the  Harvest  Season 


When  picked  up  ■ 

Left  with  husks  on,  on  the  ground 

Sept.  20 

Sept.  28 

Oct.  12 

Nov.  1 

Moldy 
culls 

Moldy  but 
passable 

Moldy 
culls 

Moldy  but 
passable 

Moldy 
culls 

Moldy  but 
passable 

Moldy 
culls 

Moldy  but 
passable 

'T.% 

■  ■•■  o'er'- '-    • 
«  /o 

15% 

16% 

'       17% 

•      17% 

13% 

43%    ' 

()90  UNIVERSITY    OP    CALIFORNIA — EXPERIMENT   STATION 

The  green  stick-tights  which  were  husked  as  soon  as  the  husks 
were  wrinkled  slightly  and  before  they  decayed,  showed  only  3  per 
cent  total  moldy  nuts,  while  the  kernels  were  notably  white  and  of 
fine  quality.  After  lying  on  the  ground  through  the  harvest  season 
the  total  mold  was  56  per  cent  instead  of  3  per  cent.  Practically 
all  the  kernels  were  amber  or  black  at  the  last  sampling,  and  in  fact, 
the  whole  lot  were  culls  pure  and  simple.  The  outside  of  the  shell, 
except  for  a  little  stain,  showed  no  clue  to  the  condition  of  the  meats. 
Green  stick-tights,  handled  somewhat  as  in  this  experiment,  produce 
many  of  the  near-grades  and  culls.  They  account  for  more  trouble 
than  the  black,  dry  stick-tights  on  the  trees,  for  the  latter,  as  noted 
before,  may  have  50  per  cent  of  good  meats.  In  France  the  nuts 
are  gathered  green  and  husked,  and  are  seldom  moldy.  This  is 
in  harmony  with  the  above  observations  and  probably  accounts  for 
the  lack  of  mold  in  the  French  nuts.  The  colored  cuts  in  figure  1 
are  presented  to  show  the  change  in  grade  of  the  nuts  due  to  the 
white  kernels  of  a  green  stick-tight  turning  to  amber  or  black, 
if  the  husk  is  allowed  to  stay  on  it  until  it  becomes  mushy.  Cuts 
a,  b,  and  c  show  the  progress  of  discoloration  in  a  lot  of  nuts  picked 
up  from  one  tree  at  the  same  time  but  divided  into  three  classes: 
a,  firm  green  stick-tights;  b,  green  stick-tights  starting  to  soften; 
c,  mushy  stick-tights.  The  amount  of  mold  in  these  classes  cannot 
be  shown  by  the  photographs;  the  total  per  cent  of  moldy  nuts  in 
the  above  classes  at  the  time  the  nuts  were  picked  up  was  as  follows : 
0,  24  and  88  per  cent,  respectively.  The  nuts  shown  in  cut  d,  were 
firm  green  stick-tights  taken  from  the  same  lot  of  nuts  as  lot  a  at 
the  time  of  picking,  but  left  on  the  ground  until  they  became  mushy. 
During  a  period  of  eleven  days  the  nuts  lay  in  the  grove  as  they 
would  under  natural  conditions  of  slack  harvesting  methods.  The 
total  mold  in  lot  d  increased  from  0  to  73  per  cent.  Meanwhile  the 
kernels  had  turned  from  first-class  white  meats,  as  shown  in  cut  a, 
to  practically  all  amber  meats  and  culls,  as  shown  in  cut  d. 


RELATION  OF  SUNBURNED  NUTS  TO  PREVALENCE 

OF  MOLD 

While  the  mold  in  stick-tights  is  under  consideration,  the  results 
of  observations  on  sunburned  nuts  may  also  be  considered,  inasmuch 
as  most  sunburned  nuts  are  also  stick-tights.  In  the  popular  mind, 
sunburning  and  mold  are  walnut  troubles  which  go  hand  in  hand. 
The  fact  that  the  extreme  cases  of  mold  are  not  necessarily  tied 
up  with  sunburned  nuts,  was  shown  without  question  during  the 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS 


691 


present  season.  Most  of  the  sunburned  nuts  drop  with  the  green 
shucks  on,  showing  a  black  spot  on  one  side  of  them.  Frequently 
the  shucks  are  not  cracked  on  such  nuts,  and  seldom  do  they  crack 
open  enough  to  let  the  nut  fall  off  the  tree  free  from  the  shuck.  The 
sunburned  nuts  often,  in  reality,  are  one  form  of  the  green  stick- 
tights.  Several  large  lots  of  these  nuts  were  gathered  and  cracked 
periodically,  to  see  if  the  mold  was  an  unfailing  partner  to  the 
sunburning  on  the  nut.  Table  7  summarizes  an  experiment  which 
will  illustrate  the  trend  of  all  similar  tests. 


TABLE  7 
Showing  Increase  of  Mold  in  Sunburned  Nuts  by  Delaying  Harvest 


Percentage  of  moldy  nuts 

Method  of  handling 

Moldy 
culls 

Moldy 
passable 

Total 
moldy 

Cracked  as  picked  up  (Sept.  29) 

16 

8 

24 

Shucked  and  cured  in  trays   (cracked 
Oct.  12)  

14 

6 

20 

Left  in  grove  with  shucks  on  (cracked 
Oct.  12) 

32 

13 

45 

Left  in  grove  with  shucks  on  (cracked 

Nov.  1) 

37 

28 

65 

There  is  no  question  but  that  sunburned  nuts,  as  they  are  gathered 
under  normal  harvesting  conditions,  are  apt  to  be  moldy,  but  it  is 
equally  clear  that  good  marketable  lots  of  near-grades  can  be  made 
out  of  such  nuts,  if  they  are  picked  up  promptly,  shucked  and  cured 
normally.  On  the  other  hand,  throwing  such  nuts  up  against  the 
trees  to  be  left  there  until  they  become  mushy  and  shuck  easier, 
will  make  culls  out  of  practically  the  whole  lot,  with  the  mold  increas- 
ing from  25  per  cent  up  to  65  per  cent  or  more. 

In  connection  with  this  table  the  question  may  be  raised,  wiry 
the  cured  nuts  showed  less  mold  than  those  cracked  when  they  were 
picked  up.  It  has  been  consistently  noticed  that  the  same  degree 
of  mold  shows  up  less  in  a  thoroughly  cured  nut  than  in  a  green 
one.  A  small  percentage  of  any  lot  of  nuts  will  pass  as  practically 
sound  when  thoroughly  cured  which  would  be  at  least  "moldy  but 
passable"  if  judged  before  curing. 

A  sunburned  nut  is  usually  characterized  by  having  one-half  of 
the  kernel  blackened  by  the  sun  injury.  For  this  reason  they  should 
not  be  mixed  with  the  good  nuts,  regardless  of  the  presence  of 
mold.     Although  they  might  possibly  be  graded  as  near-grades,  they 


692 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


will  not  be  a  very  commendable  lot.  Possibly  such  nuts  should  be 
kept  separate  in  the  grove,  and  sent  to  the  cracking  plant  as  culls, 
rather  than  lower  the  grade  of  good  nuts  by  being  intermixed  with 
them. 

EELATION  OF  CUEING  TO  PEECENTAGE  OF  MOLDY  NUTS 

Clean  nuts  harvested  in  the  ordinary  manner  are  not  likely  to  show 
any  change  in  the  percentage  of  moldy  nuts  due  to  any  methods 
of  curing. 

Table  8  shows  the  result  of  a  test  taken  in  1920.  Clean  nuts, 
harvested  by  ordinary  methods,  from  the  second  picking  were  used 
for  this  test.  Possibly  some  of  these  nuts  had  been  on  the  ground 
in  the  grove  a  week  or  more  before  they  were  harvested. 

TABLE  8 
Effect  of  Eapid  and  Slow  Curing  on  Percentage  of  Moldy  Nuts 


Moldy  culls 


Moldy  but 
passable 


Total 
moldy 


Sampled  in  grove  when  picked  up 

Cured  rapidly 

Cured  slowly -. 


7% 

8% 
7% 


8% 
8% 
9% 


15% 
16% 
16% 


The  rapidly  cured  nuts  were  spread  in  a  thin  layer  in  a  laboratory 
and  exposed  to  a  breeze  from  a  powerful  electric  fan  for  five  days. 
The  slowly  cured  ones  were  kept  for  five  days  in  paper  bags  placed 
in  a  room  where  the  humidity  was  maintained  at  nearly  100  per 
cent  for  the  entire  period.  Both  lots  were  then  exposed  to  common- 
storage  temperature  and  humidity  until  they  were  cracked.  It  is 
clear  from  the  above  summary  that  there  was  no  further  develop- 
ment of  mold  after  the  nuts  left  the  orchard.  Of  course,  all  such 
cleaned-shelled  nuts  are  partly  cured  as  they  lie  on  the  ground  in 
the  grove. 


EELATION  OF  IEEIGATION  TO  PEECENTAGE  OF  MOLDY  NUTS 

It  has  long  been  felt  that  the  bad  outbreaks  of  mold  were  asso- 
ciated in  some  way,  with  irrigation  or  cultural  practice.  Observations 
were  made  on  this  point  during  1922,  which  show  that  irrigation 
late  in  the  growing  season  to  promote  the  cracking  of  the  husks, 
making  the  nuts  drop  clean  with  few  or  no  green  stick-tights,  is 
the  first  and  most  practical  precaution  to  take  in  preventing  moldy 
nuts.     There  is  no  doubt  that  in  this  indirect  way,  that  is,  through 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OP  MOLDY  WALNUTS 


69: 


the  effect  of  irrigation  on  the  green  stick-tights,  much  of  the  trouble 
with  moldy  nuts  is  traceable  first,  to  poor  irrigation  practice,  and 
second,  to  lack  of  good  harvesting  methods. 

Table  9  shows  the  results  of  an  irrigation  trial  in  the  Anaheim 
district,  during  the  1922  season.  Both  plot  A  and  plot  C  were  well 
irrigated  up  to  the  first  of  August.  After  this  date  plot  A  received 
7  acre  inches  per  acre  on  August  8,  and  a  like  amount  on  September 
7,  while  plot  C  received  nothing.  The  rainfall  was  of  no  consequence 
from  August  1  until  the  end  of  the  harvest  season.  The  contrast 
in  the  soil  moisture  condition  in  these  two  plots  may  be  illustrated 
by  the  samples  taken  August  15  and  September  12  summarized  in 
table  9. 

The  samples  were  taken  as  soon  as  the  soil  could  be  cultivated 
following  a  heavy  irrigation. 

The  amounts  of  moisture  observed  at  these  two  periods  are  a 
close  approach  to  the  maximum  water-holding  capacity  of  the  soil 
in  plot  A  under  field  conditions. 

TABLE  9 

Comparison  Between  the  Soil  Moisture  Presents  in  Plots  A  and  C  During 

the  Latter  Part  of  the  Growing  Season  and  the  Forepart 

of  the  Harvest  Period 


Hygroscopic  point 

Ratio  of  moisture  content  to  hygroscopic  point 

Plot        Ft. 

A 

C 

Aug.  15    1922 
A                       C 

Sept.  12    1922 
A                      C 

1 
2 
3 
4 
5 
6 
7 

4.40 

2.64 
1.86 
4.71 
6.19 
3.71 
1.87 

4.69 
3.47 
6.85 
8.02 
5.32 
4.72 
3.71 

2.95 
4.03 
4.74 
2.10 
2.94 
3.37 
4.51 

1.64 
2.02 
1.90 
1.67 
1.79 
2.08 
2.83 

3.18 
4.13 
4.24 
2.48 
2.56 
3.13 
4.23 

1.22 
1.35 
1.31 
1.10 
1.50 
1.57 
1.35 

Mean 

3.52 

1.99 

3.42 

1.34 

s  The  hygroscopic  coefficient  was  determined  by  the  conventional  indirect 
method  originated  by  Briggs  and  Shantz.  A  30-gram  sample  was  used  in  all 
cases  for  this  determination. 

The  moisture  observed  is  stated  as  a  ratio  to  the  hygroscopic  coefficient. 
This  seems  to  be  the  most  effective  way  of  acquainting  the  reader  with  rela- 
tive moistures  of  the  soil.  For  the  information  of  those  not  used  to  thinking 
in  the  terms  of  present-day  soil  moisture  studies,  it  may  be  stated  that  1.47 
times  the  hygroscopic  coefficient  equals  the  wilting  point  of  annual  plants, 
while  2.71  times  the  hygroscopic  coefficient  equals  the  moisture  equivalent. 


G94 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION 


From  data  obtained  previous  to  those  presented  in  table  9,  it 
is  certain  that  the  soil  moisture  in  both  plots  A  and  C  averaged 
above  the  wilting  point  throughout  the  first  part  of  the  growing 
season,  April  to  July  inclusive.  From  the  first  of  August  on,  the 
soil  moisture  in  plot  A  was  kept  well  above  the  wilting  point.  Some 
time  about  the  first  of  September,  the  soil  of  plot  C  had  reached 
a  dryness  which  would  have  caused  annual  plants  to  wilt  and  was 
approaching  the  hygroscopic  point  by  the  middle  of  September. 

The  contrast  in  soil  moisture  was  clearly  reflected  in  the  maturity 
of  the  trees.  The  trees  in  plot  A  remained  green  throughout  the 
harvest  period  of  September  and  October.  Probably  less  than  10 
per  cent  of  the  leaves  had  dropped  by  October  30. 

In  contrast  to  this,  the  leaves  began  to  drop  from  the  trees  on 
plot  C  during  the  middle  of  September,  and  by  October  30  many  of 
the  trees  were  entirely  bare  of  foliage.  Probably  90  per  cent  of  the 
leaves  of  the  plot  were  on  the  ground  at  this  last  mentioned  date. 


TABLE  10 
Connection  Between  Lack  of  Water  in  the  Late  Summer  and  Stick-Tight 

and  Moldy  Nuts 


Per  cent 

crop 

dropped  as 

stick- 
tights9 

Per  cent  of  total  crop  moldy 

Moldy 
culls 

Moldy  but 
passable 

Total 

Plot  A  (continually  well  irrigated) 

Plot  C  (dry  in  latter  part  of  August 
and  in  September) 

22% 
52% 

5% 
8% 

12% 
17% 

17% 
25% 

The  close  relationship  between  the  lack  of  soil  moisture  to  stick- 
tights,  and  thus  the  prevalence  of  moldy  nuts,  is  clearly  shown  by 
table  10. 

In  addition  to  the  culls,  due  to  mold,  the  dry  plot  produced 
about  20  per  cent  culls  because  of  black  meats  from  the  mushy  stick- 
tights.  Meanwhile  the  well-irrigated  plot  showed  less  than  10  per 
cent  additional  culls  from  all  other  causes,  and  could  easily  have 
been  graded  as  Diamond  Brand.  The  entire  crop  from  the  dry 
plot,  with  25  per  cent  culls,  would  hardly  make  the  near-grade  class. 


o  The  dried-up  black-husked  stick-tights,  discussed  on  pages  686  and  689  are 
figured  in  the  total  per  cent  of  stick-tights  for  both  plots.  During  a  year  when 
this  particular  type  of  stick-tight  was  less  prevalent,  the  contrast  in  the  per- 
centage of  stick-tights  due  to  irrigation  would  be  even  more  marked  than 
during  the  1922  season. 


BULLETIN  367]       HARVESTING  AND  IRRIGATION  OF  MOLDY  WALNUTS  695 

Each  100  pounds  of  nuts  from  the  crop  of  the  dry  plot  was  actually 
worth  at  least  $7.50  less  than  an  equal  amount  from  the  well-irrigated 
plot.  With  only  an  average  crop  of  nuts  (825  pounds  per  acre) 
this  would  mean  a  loss  of  $61.88  per  acre.  An  extra  run  of  water 
would  have  been  a  paying  investment. 

If  a  grower  has  failed  in  following  up  his  irrigation  correctly, 
he  can  still  rescue  the  crop  in  first-grade  condition  by  proper  harvest- 
ing. If  he  is  slack  in  both  of  these  practices,  there  is  a  very  small 
likelihood  of  obtaining  anything  but  near-grades  and  cull  nuts. 


SUMMAEY 

The  work  has  shown  conclusively  that  nuts  will  mold  readily 
on  the  trees  at  any  time  after  the  husks  start  to  crack,  the  mold 
starting  its  growth  on  the  damp  lining  of  the  husk  and  finally  spread- 
ing to  the  kernel.  The  vast  majority  of  the  nuts  which  are  going 
to  be  moldy  are  in  this  condition  before  they  reach  the  curing  yards. 
The  mold  makes  nearly  all  its  growth  while  the  kernels  are  still 
very  moist.  The  first  drying  out  at  the  beginning  of  the  curing 
process  checks  any  further  development.  The  percentage  of  moldy 
nuts  increases  rapidly  if  the  harvesting  operations  are  delayed, 
especially  if  the  nuts  are  still  in  the  husks,  even  though  they  are 
partly  cracked  open  and  still  on  the  trees.  The  percentage  of  moldy 
nuts  is  greater  in  stick-tights  than  in  clean  nuts.  As  the  harvest 
season  advances,  the  increase  of  mold  is  more  pronounced  in  stick- 
tights  than  in  clean  nuts.  The  increase  in  percentage  of  mold  among 
nuts  left  in  the  orchard  is  much  greater  in  the  case  of  green  and 
mushy  stick-tights,  than  in  the  case  of  black,  dry  stick-tights,  since 
the  latter  dry  up  and  partly  cure  while  still  on  the  trees.  The 
percentage  of  the  crop  which  falls  as  green  or  mushy  stick-tights 
is  much  greater  in  groves  which  were  not  adequately  irrigated  during 
the  very  last  portion  of  the  growing  season. 

PEACTICAL  KECOMMENDATIONS 

1.  Use  enough  late  summer  irrigation  water  so  the  trees  hold  their 
leaves  through  the  harvest  season,  and  the  nuts  drop  free  from  the 
husks. 

2.  Hasten  the  harvest  in  general;  shake  the  trees  at  the  first 
picking,  and  have  crew  enough  to  go  over  the  entire  orchard  once 
a  week,  shaking  the  trees  each  time. 


696  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

3.  Any  trees  that  show  a  tendency  to  produce  green  stick-tights 
should  be  stripped  of  the  crop  the  first  time  over  and  husked  by 
hand,  if  necessary.  Such  nuts  will  have  to  be  husked  sometime; 
if  they  are  taken  in  time  they  will  be  first-grade  nuts,  but  if  they 
are  neglected,  and  the  husks  become  mushy,  they  will  be  culls. 

4.  Knock  off  all  the  black  stick-tights  at  the  first  picking,  and 
husk  them  promptly. 

5.  Keep  all  the  dry  stick-tights,  mushy  stick-tights  and  sunburned 
nuts  separate  from  the  rest  of  the  crop  in  the  grove  and  curing  yards, 
and  deliver  them  to  the  packing-house  separately.  They  are  only 
near-grades  at  the  best,  and  if  they  are  kept  separate  from  the  rest 
of  the  crop,  it  will  save  much  money  and  trouble  in  the  packing- 
house not  to  have  to  attempt  to  pick  them  out  of  the  better  nuts. 
Furthermore,  if  the  grower  mixes  too  many  of  the  black  and  mushy 
stickers  in  with  the  clean-shelled  nuts,  the  whole  lot  may  have  to 
go  as  near-grades.  Any  attempt  to  fool  the  packing-house  manager, 
by  mixing  good  nuts  with  poor  ones  or  vice  versa,  is  very  short 
sighted,  not  only  for  the  immediate  financial  returns  of  the  grower 
but  for  the  good  name  of  California  walnuts.  It  is  the  first  duty 
of  the  packing-house  manager  to  grade  the  poor  nuts  out  of  the 
good  ones,  so  don't  add  to  his  duties  and  the  growers'  expense  by 
knowingly  letting  nuts  with  a  high  percentage  of  mold  get  in  with 
the  good  lots. 

6.  The  mold  in  walnuts  is  there,  in  the  great  majority  of  cases, 
before  they  reach  the  curing  trays.  Under  any  reasonably  good 
method  of  handling  the  nuts  on  the  trays,  the  mold  will  not  increase 
during  the  curing  process. 


STATION  PUBLICATIONS  AVAILABLE  FOB  FBEE  DISTRIBUTION 


No. 

253. 

261. 

262. 

263. 
268. 
270. 


273. 

275. 

276. 
277. 
278. 
279. 
280. 

283. 
285. 
286. 
287. 
294. 
298. 
304. 

308. 


312. 
317. 

319. 
321. 
324. 

325. 


828. 
331. 
334. 


BULLETINS 

No. 

Irrigation   and   Soil  Conditions  in  the  335. 

Sierra  Nevada  Foothills,  California. 

Melaxuma    of    the    Walnut,    "Juglans  336. 

regia." 

Citrus   Diseases   of   Florida   and   Cuba  339. 

Compared  with  those  of  California. 

Size  Grades  for  Ripe  Olives.  341. 

Growing  and  Grafting  Olive  Seedlings  343. 

A  Comparison  of  Annual  Cropping,  Bi-  344. 

ennial  Cropping,  and  Green  Manures 
on  the  Yield  of  Wheat.  347. 

Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain.  348. 

The  Cultivation  of  Belladonna  in  Cali-  349. 

fornia. 

The   Pomegranate.  350. 

Sudan  Grass.  351. 

Grain   Sorghums.  352. 

Irrigation  of  Rice  in  California. 

Irrigation  of  Alfalfa  in  the  Sacramento  353. 

Valley.  354. 

The  Olive  Insects  of  California.  355. 

The  Milk  Goat  in  California.  357. 

Commercial    Fertilizers. 

Vinegar  from  Waste  Fruits. 

Bean    Culture   in    California.  358. 

Seedless  Raisin  Grapes. 

A  Study  of  the  Effects  of  Freezes  on  359. 

Citrus   in   California.  360. 

I.  Fumigation  with  Liquid  Hydrocyanic 
Acid.  II.  Physical  and  Chemical  Prop-  361. 

erties  of  Liquid  Hydrocyanic  Acid. 

Mariout   Barley.  362. 

Selections  of   Stocks  in  Citrus   Propa-  363. 

gation. 

Caprifigs  and  Caprification.  364. 

Commercial  Production  of  Grape  Syrup. 

Storage  of  Perishable  Fruit  at  Freezing  365. 

Temperatures.  366. 

Rice  Irrigation  Measurements  and  Ex- 
periments    in     Sacramento     Valley,  368 
1914-1919. 

Prune  Growing  in  California.  369. 

Phylloxera-Resistant  Stocks. 

Preliminary  Volume  Tables  for  Second- 
Growth  Redwood. 


Cocoanut   Meal    as    a   Feed   for   Dairy 
Cows  and  Other  Livestock. 

The   Preparation  of  Nicotine  Dust  as 
an  Insecticide. 

The  Relative  Cost  of  Making  Logs  from 
Small    and   Large   Timber. 

Studies  on  Irrigation  of  Citrus  Groves. 

Cheese  Pests  and  Their  Control. 

Cold  Storage  as  an  Aid  to  the  Market- 
ing of  Plums. 

The  Control  of  Red  Spiders  in  Decidu- 
ous Orchards. 

Pruning  Young  Olive  Trees. 

A    Study    of    Sidedraft    and    Tractor 
Hitches. 

Agriculture  in  Out-over  Redwood  Lands. 

California  State  Dairy  Cow  Competition. 

Further  Experiments  in  Plum  Pollina- 
tion. 

Bovine  Infectious  Abortion. 

Results  of  Rice  Experiments  in   1922. 

The  Peach  Twig  Borer. 

A    Self-mixing    Dusting    Machine 
Applying      Dry       Insecticides 
Fungicides. 

Black    Measles,    Water    Berries, 
Related    Vine   Troubles. 

Fruit  Beverage  Investigations. 

Gum  Diseases  of  Citrus  Trees  in 
fornia. 

Preliminary   Yield   Tables   for   Second 
Growth  Redwood. 

Dust  and  the  Tractor  Engine. 

The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal    Dusts   for   the    Control   of 
Bunt. 

Avocado  Culture  in  California. 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Bacterial  Decomposition  of  Olives  dur- 
ing Pickling. 

Comparison  of  Woods  for  Butter  Boxes. 


for 
and 


and 


Cali- 


CIRCULARS 
No.  No. 
70.  Observations   on    the    Status   of    Corn  iei. 
Growing  in  California.  164. 
87.  Alfalfa.  165. 
111.  The  Use  of  Lime  and  Gypsum  on  Cali- 
fornia Soils.  166. 
113.  Correspondence  Courses  in  Agriculture.  167. 
117.  The    Selection    and    Cost   of    a    Small  170. 

Pumping  Plant. 

127.  House  Fumigation.  172. 

129.  The  Control  of  Citrus  Insects.  173. 
136.  Melilotus   indica    as    a    Green-Manure 

Crop  for  California.  174. 

144.  Oidium  or  Powdery  Mildew  of  the  Vine.  175. 

151.  Feeding  and  Management  of  Hogs. 

152.  Some  Observations  on  the  Bulk  Hand-  178. 

ling  of  Grain  in  California.  179. 

153.  Announcement  of  the  California  State 

Dairy  Cow  Competition,  1916-18.  182. 

154.  Irrigation  Practice  in  Growing  Small 

Fruit  in  California.  184. 

155.  Bovine  Tuberculosis.  188. 
157.  Control  of  the  Pear  Scab.  190. 

159.  Agriculture  in  the  Imperial  Valley.  193. 

160.  Lettuce  Growing  in  California.  198. 


Potatoes  in  California. 

Small  Fruit  Culture  in  California. 

Fundamentals   of   Sugar   Beet   Culture 

under  California  Conditions. 
The  County  Farm  Bureau. 
Feeding  Stuffs  of  Minor  Importance. 
Fertilizing  California  Soils  for  the  1918 

Crop. 
Wheat  Culture. 
The    Construction    of    the    Wood-Hoop 

Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution  of  Milk. 
The  Packing  of  Apples  in  California. 
Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
Extending  the  Area  of  Irrigated  Wheat 

in   California  for  1918. 
A  Flock  of  Sheep  on  the  Farm. 
Lambing  Sheds. 

Agriculture  Clubs  in  California. 
A  Study  of  Farm  Labor  in  California. 
Syrup  from  Sweet  Sorghum. 


CI  RC  U  LARS — Continued 


No. 
199. 
201. 
202. 

203. 
205. 
206. 
208. 

209. 
210. 
212. 
214. 

215. 
217. 

218. 

219. 
224. 


228. 
230. 

231. 
232. 

233. 
234. 

235. 

236. 

237. 

238. 
239. 

240. 


Onion  Growing  in  California. 

Helpful  Hints  to  Hog  Raisers. 

County  Organizations  for  Rural  Fire 
Control. 

Peat  as  a  Manure  Substitute. 

Blackleg. 

Jack  Cheese. 

Summary  of  the  Annual  Reports  of  the 
Farm  Advisors  of  California. 

The  Function  of  the  Farm  Bureau. 

Suggestions  to  the  Settler  in  California. 

Salvaging  Rain-Damaged  Prunes. 

Seed  Treatment  for  the  Prevention  of 
Cereal  Smuts. 

Feeding  Dairy  Cows  in  California. 

Methods  for  Marketing  Vegetables  in 
California. 

Advanced  Registry  Testing  of  Dairy 
Cows. 

The  Present  Status  of  Alkali. 

Control  of  the  Brown  Apricot  Scale 
and  the  Italian  Pear  Scale  on  Decid- 
uous Fruit  Trees. 

Vineyard  Irrigation  in  Arid  Climates. 

Testing  Milk,  Cream,  and  Skim  Milk 
for  Butterfat. 

The  Home  Vineyard. 

Harvesting  and  Handling  California 
Cherries  for  Eastern  Shipment. 

Artificial  Incubation. 

Winter  Injury  to  Young  Walnut  Trees 
during  1921-22. 

Soil  Analysis  and  Soil  and  Plant  Inter- 
relations. 

The  Common  Hawks  and  Owls  of  Cali- 
fornia from  the  Standpoint  of  the 
Rancher. 

Directions  for  the  Tanning  and  Dress- 
ing of  Furs. 

The  Apricot  in  California. 

Harvesting  and  Handling  Apricots  and 
Plums  for  Eastern  Shipment. 

Harvesting  and  Handling  Pears  for 
Eastern  Shipment. 


No. 
241. 

242. 
243. 

244. 
245. 
247. 
248. 

249. 
250. 

251. 


252. 
253. 
254. 

255. 

256. 
257. 
258. 
259. 
260. 

261. 
262. 
263. 
264. 

265. 
266. 

267. 

270. 
271. 


Harvesting  and  Handling  Peaches  for 
Eastern  Shipment. 

Poultry  Feeding. 

Marmalade  Juice  and  Jelly  Juice  from 
Citrus  Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine  Pruning  Systems. 

Colonization  and  Rural  Development. 

Some  Common  Errors  in  Vine  Pruning 
and  Their  Remedies. 

Replacing  Missing  Vines. 

Measurement  of  Irrigation  Water  on 
the  Farm. 

Recommendations  Concerning  the  Com- 
mon Diseases  and  Parasites  of 
Poultry   in   California. 

Supports  for  Vines. 

Vineyard  Plans. 

The  Use  of  Artificial  Light  to  Increase 
Winter  Egg  Production. 

Leguminous  Plants  as  Organic  Fertil- 
izer in  California  Agriculture. 

The  Control  of  Wild  Morning  Glory. 

The  Small-Seeded  Horse  Bean. 

Thinning  Deciduous  Fruits. 

Pear  By-products. 

A  Selected  List  of  References  Relating 
to  Irrigation  in  California. 

Sewing  Grain  Sacks. 

Cabbage  Growing  in  California. 

Tomato  Production  in  California. 

Preliminary  Essentials  to  Bovine  Tuber- 
culosis Control. 

Plant  Disease  and  Pest  Control. 

Analyzing  the  Citrus  Orchard  by  Means 
of  Simple  Tree  Records. 

The  Tendency  of  Tractors  to  Rise  in 
Front;  Causes  and  Remedies. 

A  Farm  Septic  Tank. 

Brooding  Chicks  Artificially. 


